Two general types of automatic tape cartridge playing machines have been used in the radio broadcasting industry prior to this invention. These are random access machines and instant access machines.
The random access type moved cartridges back and forth between a storage unit and a single playback unit. This was made in two configurations.
The first random access configuration was a carousel machine. Typically, it had a drum storing 24 cartridges. The drum turned until the selected cartridge was located in front of the playback unit. The cartridge was then inserted into the playback unit in readiness for playing. After playing, it was returned to the drum which then rotated to place the next selected cartridge in front of the playback unit.
The second random access configuration, no longer made, stored about 55 cartridges in a vertical stack. A playback unit was mounted behind the stack on an elevatable platform. This was moveable up and down until it stopped at a selected cartridge. The cartridge was inserted into the playback unit and played after which it was returned to the stack and the unit was then moved to the next selected cartridge.
The problem of using random access machines in broadcasting is that a single machine cannot play cartridges one immediately after the other. In order to partially overcome this problem, multiple random access machines can be used. However it is very difficult to program multiple random access machines with the limitation that one cartridge cannot be played immediately after another in any one playback unit.
It is possible to solve this problem by putting duplicate cartridges in two different machines. Then one is never faced with the back-to-back playout of one machine. The cost of recording duplicate program material makes this very expensive.
The other type of machine, the instant access machine, comprises, in effect, multiple playback units, each with a cartridge ready to be played instantly on command. A typical machine consists of 48 cartridge-supporting trays, 48 heads, 48 pinch rollers and 48 amplifiers. This overcomes the above described limitation of the random access machine but is very costly. The cost of a single 48-tray instant access machine is more than 10,000, yet it would be woefully inadequate to handle the large volume of cartridges used in modern broadcasting. Cost and service problems are major handicaps.
In short, prior to the present invention, no practical automatic tape cartridge playing machine or system has been available for modern broadcasting. Neither the conventional random access machine nor the instant access machine can function suitably except with modifications and duplications of components which would make it prohibitively expensive both with respect to original investment and cost of maintenance.